1
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Pashikanti G, Chavan LN, Liebeskind LS, Goodman MM. Synthetic Efforts toward the Synthesis of a Fluorinated Analog of 5-Aminolevulinic Acid: Practical Synthesis of Racemic and Enantiomerically Defined 3-Fluoro-5-aminolevulinic Acid. J Org Chem 2024; 89:12176-12186. [PMID: 39189689 PMCID: PMC11382157 DOI: 10.1021/acs.joc.4c01070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2024] [Revised: 08/08/2024] [Accepted: 08/15/2024] [Indexed: 08/28/2024]
Abstract
In 2017, the FDA authorized 5-aminolevulinic acid (5-ALA) for intraoperative optical imaging of suspected high-grade gliomas. This was the first authorized optical imaging agent for brain tumor surgery to enhance the visualization of malignant tissue. Herein we report the synthesis of a racemic and enantiopure fluorinated analog of 5-ALA, i.e., 3-fluoro-5-aminolevulinic acid (3F-5-ALA). We anticipate that these studies will provide the foundation for the future construction of a fluorine-18-labeled 5-ALA PET tracer to be used for functional and metabolic imaging of gliomas.
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Affiliation(s)
- Gouthami Pashikanti
- Department
of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Lahu N. Chavan
- Department
of Radiology and Imaging Sciences, School of Medicine, Emory University, 1364 Clifton Road NE, Atlanta, Georgia 30322, United States
- Center
for Systems Imaging, Emory University, 1841 Clifton Rd NE, Atlanta, Georgia 30322, United States
| | - Lanny S. Liebeskind
- Department
of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Mark M. Goodman
- Department
of Radiology and Imaging Sciences, School of Medicine, Emory University, 1364 Clifton Road NE, Atlanta, Georgia 30322, United States
- Center
for Systems Imaging, Emory University, 1841 Clifton Rd NE, Atlanta, Georgia 30322, United States
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2
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Trojan M, Hroch A, Gruden E, Cvačka J, Čejka J, Tavčar G, Rybáčková M, Kvíčala J. Modified aryldifluorophenylsilicates with improved activity and selectivity in nucleophilic fluorination of secondary substrates. RSC Adv 2024; 14:22326-22334. [PMID: 39010913 PMCID: PMC11247957 DOI: 10.1039/d4ra04332d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2024] [Accepted: 07/04/2024] [Indexed: 07/17/2024] Open
Abstract
Nucleophilic fluorination of secondary aliphatic substrates, especially of halides, still remains a challenge. Among the available reagents, TBAT belongs to one of the best choices due to its stability, affordable price and low toxicity. With the aim to improve its selectivity, we synthesized three analogues modified in the aryl part of the TBAT reagent with one or two electron donating methoxy groups or with one electron withdrawing trifluoromethyl group. All three reagents are air-stable compounds and their structure was confirmed by a single crystal X-ray analysis. In testing the reactivity and selectivity of the reagents with a library of secondary bromides, as well as of other selected primary and secondary substrates, we found that substitution with methoxy groups mostly improves both reactivity and selectivity compared to TBAT, while the substitution with trifluoromethyl group leads to inferior results. Difluorosilicates modified by more than two electron donating methoxy groups proved to be unstable and decomposed spontaneously to the HF2 - anion. DFT calculations of tetramethylammonium analogues of the studied reagents disclosed that the substitution of the phenyl group with the methoxy substituent lowers the transitions state energy of the decomposition to a fluorosilane-fluoride complex, while the substitution with the trifluoromethyl group has an opposite effect.
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Affiliation(s)
- Michal Trojan
- Department of Organic Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 Czech Republic
| | - Adam Hroch
- Department of Organic Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 Czech Republic
| | - Evelin Gruden
- Department of Inorganic Chemistry and Technology, "Jožef Stefan" Institute Jamova Cesta 39 Ljubljana Slovenia
| | - Josef Cvačka
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences Flemingovo Náměstí 542/2 160 00 Prague 6 Czech Republic
| | - Jan Čejka
- Department of Solid State Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 Czech Republic
| | - Gašper Tavčar
- Department of Inorganic Chemistry and Technology, "Jožef Stefan" Institute Jamova Cesta 39 Ljubljana Slovenia
| | - Markéta Rybáčková
- Department of Organic Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 Czech Republic
| | - Jaroslav Kvíčala
- Department of Organic Chemistry, University of Chemistry and Technology, Prague Technická 5 166 28 Prague 6 Czech Republic
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3
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Rufino VC, Pliego JR. Bifunctional iminophosphorane organocatalyst with additional hydrogen bonding: Calculations predict enhanced catalytic performance in a michael addition reaction. J Mol Graph Model 2024; 129:108760. [PMID: 38513601 DOI: 10.1016/j.jmgm.2024.108760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 02/29/2024] [Accepted: 03/11/2024] [Indexed: 03/23/2024]
Abstract
A new iminophosphorane-thiourea superbase was rationally designed and investigated as an organocatalyst for the enantioselective Michael addition reaction of nitromethane to 4-phenylbut-3-en-2-one. Starting from an iminophosphorane-thiourea organocatalyst structure already known, we have used theoretical calculations to determine the structures of transition states involved in the carbon-carbon bond formation step and carried out structural modifications to accelerate the reaction rate and to increase the enantioselectivity. The effective structural modification was adding a rigid hydroxyl group able to make an additional hydrogen bond to the transition state, producing a substantial decrease of the ΔG‡ by 7 kcal mol-1. The enantiomeric excess is predicted to be above of 97% using the reliable M06-2X and ωB97M - V functionals. The determination of the complete reaction mechanism and free energy profile was followed by a detailed microkinetic analysis. The present study points out a new direction for structural modifications on this kind of organocatalyst.
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Affiliation(s)
- Virginia C Rufino
- Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, 36301-160, São João del-Rei, MG, Brazil
| | - Josefredo R Pliego
- Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, 36301-160, São João del-Rei, MG, Brazil.
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4
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Trojan M, Kučnirová K, Bouzková Š, Cvačka J, Čejka J, Tavčar G, Rybáčková M, Kvíčala J. Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents. Org Biomol Chem 2024; 22:1047-1056. [PMID: 38197465 DOI: 10.1039/d3ob01875j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2024]
Abstract
TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions. To eliminate the possibility of hydrogen fluoride elimination in the above reagents, we prepared four quaternary ammonium fluorides lacking β-elimination possibility in the hydrocarbon chain, transformed them to the corresponding difluorotriphenylsilicates, and compared their reactivity with that of the commercial reagents. Furthermore, attempts to isolate analogous tetrabutylammonium difluoromethyldiphenylsilicate or difluorodimethylphenylsilicate failed, as was confirmed by comparison of the published experimental data with computed 19F NMR spectra. Finally, we studied the transition states of decomposition of various tetramethylammonium methylphenyldifluorosilicates by DFT methods and found that their relative energies increase with an increasing number of phenyl groups. The formation of difluorosilicates is a nearly barrierless process.
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Affiliation(s)
- Michal Trojan
- Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic.
| | - Kateřina Kučnirová
- Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic.
| | - Šárka Bouzková
- Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic.
| | - Josef Cvačka
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí 542/2, 160 00 Prague 6, Czech Republic
| | - Jan Čejka
- Department of Solid State Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic
| | - Gašper Tavčar
- Department of Inorganic Chemistry and Technology, "Jožef Stefan" Institute, Jamova cesta 39, Ljubljana, Slovenia
| | - Markéta Rybáčková
- Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic.
| | - Jaroslav Kvíčala
- Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic.
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5
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Nucleophilic Reactions Using Alkali Metal Fluorides Activated by Crown Ethers and Derivatives. Catalysts 2023. [DOI: 10.3390/catal13030479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2023] Open
Abstract
We review crown ether-facilitated nucleophilic reactions using metal salts, presenting the studies using kinetic measurements and quantum chemical methods. We focus on the mechanistic features, specifically on the contact ion-pair (CIP) mechanism of metal salts for nucleophilic processes promoted by crown ethers and derivatives. Experimental verification of the CIP form of the metal salt CsF complexed with [18-Crown-6] by H-NMR spectroscopy is described. The use of chiral crown ethers and derivatives for enantioselective nucleophilic processes is also discussed.
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6
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Crown Ether as Organocatalyst for Reductive Upgrading of CO2 to N-Containing Benzoheterocyclics and N-Formamides. J Catal 2023. [DOI: 10.1016/j.jcat.2023.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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7
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Oh YH, Kim DW, Lee S. Ionic Liquids as Organocatalysts for Nucleophilic Fluorination: Concepts and Perspectives. Molecules 2022; 27:5702. [PMID: 36080470 PMCID: PMC9457570 DOI: 10.3390/molecules27175702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 08/30/2022] [Accepted: 09/01/2022] [Indexed: 11/16/2022] Open
Abstract
Besides their extremely useful properties as solvent, ionic liquids (ILs) are now considered to be highly instructive tools for enhancing the rates of chemical reactions. The ionic nature of the IL anion and cation seems to be the origin of this fascinating function of ILs as organocatalyst/promoter through their strong Coulombic forces on other ionic species in the reaction and also through the formation of hydrogen bonds with various functional groups in substrates. It is now possible to tailor-make ILs for specific purposes as solvent/promoters in a variety of situations by carefully monitoring these interactions. Despite the enormous potentiality, it seems that the application of ILs as organocatalysts/promoters for chemical reactions have not been fully achieved so far. Herein, we review recent developments of ILs for promoting the nucleophilic reactions, focusing on fluorination. Various aspects of the processes, such as organocatalytic capability, reaction mechanisms and salt effects, are discussed.
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Affiliation(s)
- Young-Ho Oh
- Department of Applied Chemistry, Kyung Hee University, Duckyoung-daero 1732, Yongin City 446-701, Korea
| | - Dong Wook Kim
- Department of Chemistry, Inha University, 100 Inha-ro, Nam-gu, Incheon 402-751, Korea
| | - Sungyul Lee
- Department of Applied Chemistry, Kyung Hee University, Duckyoung-daero 1732, Yongin City 446-701, Korea
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8
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Khandelwal M, Pemawat G, Khangarot RK. Recent Developments in Nucleophilic Fluorination with Potassium Fluoride (KF): A Review. ASIAN J ORG CHEM 2022. [DOI: 10.1002/ajoc.202200325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Manisha Khandelwal
- Mohanlal Sukhadia University Department of Chemistry UCOS, Durga Nursery Road 313001 Udaipur INDIA
| | - Gangotri Pemawat
- Mohanlal Sukhadia University Department of Chemistry UCOS, Durga Nursery Road 313001 Udaipur INDIA
| | - Rama Kanwar Khangarot
- Mohanlal Sukhadia University Department of Chemistry UCOS, Durga Nursery Road 313001 Udaipur INDIA
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9
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Lisboa FM, Pliego JR. S N2 versus E2 reactions in a complex microsolvated environment: theoretical analysis of the equilibrium and activation steps of a nucleophilic fluorination. J Mol Model 2022; 28:159. [PMID: 35596807 DOI: 10.1007/s00894-022-05160-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Accepted: 05/12/2022] [Indexed: 10/18/2022]
Abstract
The reactivity of the fluoride ion towards alkyl halides is highly dependent on the solvating environment. In polar aprotic solvents with large counter-ions is highly reactive and produces substantial E2 product, whereas in polar protic solvents leads to slow kinetics and high selectivity for SN2 reactions. The use of a more complex environment with stoichiometric addition of tert-butanol to acetonitrile solvent is able to module the reactivity and selectivity of tetrabutylammonium fluoride (TBAF). In the present work, we have performed a detailed theoretical analysis of this complex reaction system by density functional theory, continuum solvation model, and including explicit tert-butanol molecules. A kinetic model based on the free energy profile was also used to predict the reactivity and selectivity. The results indicated that the TBAF(tert-butanol) complex plays the key role to increase the SN2 selectivity, whereas higher aggregates are not relevant. The E2 product is formed exclusively via free TBAF, because the solvating tert-butanol in the TBAF(tert-butanol) complex inhibits the E2 pathway. Our analysis suggests that diols or tetraols could produce an improved selectivity.
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Affiliation(s)
- Fernando M Lisboa
- Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, MG, 36301-160, Brazil
| | - Josefredo R Pliego
- Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, MG, 36301-160, Brazil.
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10
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Copper-Mediated Aromatic Fluorination Using N-Heterocycle-Carbene Ligand: Free Energy Profile of the Cu(I)/Cu(III) and Cu(II) radical Mechanisms. J Organomet Chem 2022. [DOI: 10.1016/j.jorganchem.2022.122397] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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11
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Liu ZL, Xu JX, Deng N, Dong Z, Shen X, Xu J, Xu HJ. Coupling of Thiols and Aryl Halides Mediated by Dicyclohexano-18-Crown-6 and Potassium Carbonate. Curr Org Synth 2022; 19:824-837. [PMID: 35418286 DOI: 10.2174/1570179419666220412084111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 01/26/2022] [Accepted: 02/03/2022] [Indexed: 11/22/2022]
Abstract
AIMS A simple, transition-metal-free C-S coupling protocol for the synthesis of aryl thioethers is reported Background: Sulfur-containing moieties are ubiquitous in pharmaceutical drugs and materials and therefore methods for their construction are of great importance. One approach entails the catalytic coupling of an aryl halohydrocarbon with a thiol, but the transition metal catalysts usually used are prone to poisoning by participating sulfur species and efficient catalysis is usually only achieved after complex ligand optimization. OBJECTIVE New transition-metal-free approaches to the synthesis of C-S bonds are urgently need Method: We screened the reaction conditions such as alkali, crown ether, solvent, temperature, etc., tested the compatibility of the reaction substrate, and analyzed the mechanism process. RESULT the optimized reaction conditions were determined to be 1.0 equiv of aryl halides and 1.2 equiv of thiols at 110 ℃ in toluene with K2CO3 (1.5 equiv) as a base, promoted by 10 mol% dicyclohexano-18-crown-6. Up to 33 examples of thioethers were synthesized under transition-metal-free conditions in good to excellent yields. CONCLUSION we have developed a simple and efficient method for the C-S cross-coupling of a wide variety of (hetero)aryl halides and thiols mediated by dicyclohexano-18-crown-6 and without the need for transition-metal catalyst. In addition, the preparation and gram-scale experiments of a variety of drug molecules further verify the practicability of our developed method.
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Affiliation(s)
- Zhong-Lin Liu
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Jing-Xiu Xu
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Ning Deng
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Zheng Dong
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Xiao Shen
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Jun Xu
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
| | - Hua-Jian Xu
- School of Food and Biological Engineering, School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Advance Catalytic Materials and Reaction Engineering, Hefei University of Technology, Hefei 230009, China
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12
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Pupo G, Gouverneur V. Hydrogen Bonding Phase-Transfer Catalysis with Alkali Metal Fluorides and Beyond. J Am Chem Soc 2022; 144:5200-5213. [PMID: 35294171 PMCID: PMC9084554 DOI: 10.1021/jacs.2c00190] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Phase-transfer catalysis (PTC) is one of the most powerful catalytic manifolds for asymmetric synthesis. Chiral cationic or anionic PTC strategies have enabled a variety of transformations, yet studies on the use of insoluble inorganic salts as nucleophiles for the synthesis of enantioenriched molecules have remained elusive. A long-standing challenge is the development of methods for asymmetric carbon-fluorine bond formation from readily available and cost-effective alkali metal fluorides. In this Perspective, we describe how H-bond donors can provide a solution through fluoride binding. We use examples, primarily from our own research, to discuss how hydrogen bonding interactions impact fluoride reactivity and the role of H-bond donors as phase-transfer catalysts to bring solid-phase alkali metal fluorides in solution. These studies led to hydrogen bonding phase-transfer catalysis (HB-PTC), a new concept in PTC, originally crafted for alkali metal fluorides but offering opportunities beyond enantioselective fluorination. Looking ahead, the unlimited options that one can consider to diversify the H-bond donor, the inorganic salt, and the electrophile, herald a new era in phase-transfer catalysis. Whether abundant inorganic salts of lattice energy significantly higher than those studied to date could be considered as nucleophiles, e.g., CaF2, remains an open question, with solutions that may be found through synergistic PTC catalysis or beyond PTC.
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Affiliation(s)
- Gabriele Pupo
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, U.K
| | - Véronique Gouverneur
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, U.K
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Oh Y, Yun W, Lee S, Kim DW. Kinetics and Quantum Chemical Analysis of Intramolecular S
N
2 Reactions by Using Metal Salts and Promoted by Crown Ethers: Contact Ion Pair vs. Separated Nucleophile Mechanism. ChemistrySelect 2022. [DOI: 10.1002/slct.202104431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Young‐Ho Oh
- Department of Applied Chemistry Kyung Hee University 1732, Deogyeong-daero, Giheung-gu Yongin-si Gyeonggi-do 17104, Republic of Korea
| | - Wonhyuk Yun
- Department of Chemistry and Chemical Engineering Inha University 100 Inha-ro, Nam-gu Incheon 402-751, Republic of Korea
| | - Sungyul Lee
- Department of Applied Chemistry Kyung Hee University 1732, Deogyeong-daero, Giheung-gu Yongin-si Gyeonggi-do 17104, Republic of Korea
| | - Dong Wook Kim
- Department of Chemistry and Chemical Engineering Inha University 100 Inha-ro, Nam-gu Incheon 402-751, Republic of Korea
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14
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Oh YH, Shinde SS, Lee S. Nucleophilic Radiofluorination Using Tri- tert-Butanol Ammonium as a Bifunctional Organocatalyst: Mechanism and Energetics. Molecules 2022; 27:1044. [PMID: 35164308 PMCID: PMC8838713 DOI: 10.3390/molecules27031044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 01/28/2022] [Accepted: 02/01/2022] [Indexed: 02/05/2023] Open
Abstract
We present a quantum chemical analysis of the 18F-fluorination of 1,3-ditosylpropane, promoted by a quaternary ammonium salt (tri-(tert-butanol)-methylammonium iodide (TBMA-I) with moderate to good radiochemical yields (RCYs), experimentally observed by Shinde et al. We obtained the mechanism of the SN2 process, focusing on the role of the -OH functional groups facilitating the reactions. We found that the counter-cation TBMA+ acts as a bifunctional promoter: the -OH groups function as a bidentate 'anchor' bridging the nucleophile [18F]F- and the -OTs leaving group or the third -OH. These electrostatic interactions cooperate for the formation of the transition states of a very compact configuration for facile SN2 18F-fluorination.
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Affiliation(s)
- Young-Ho Oh
- Department of Applied Chemistry, Kyung Hee University, Deogyeong-daero 1732, Yongin-si 17104, Gyeonggi-do, Korea;
| | - Sandip S. Shinde
- Department of Nuclear Medicine, Molecular Imaging and Radiochemistry, Friedrich-Alexander University Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Sungyul Lee
- Department of Applied Chemistry, Kyung Hee University, Deogyeong-daero 1732, Yongin-si 17104, Gyeonggi-do, Korea;
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15
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Inter- and Intra-Molecular Organocatalysis of S N2 Fluorination by Crown Ether: Kinetics and Quantum Chemical Analysis. Molecules 2021; 26:molecules26102947. [PMID: 34063489 PMCID: PMC8156096 DOI: 10.3390/molecules26102947] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/05/2021] [Accepted: 05/12/2021] [Indexed: 11/29/2022] Open
Abstract
We present the intra- and inter-molecular organocatalysis of SN2 fluorination using CsF by crown ether to estimate the efficacy of the promoter and to elucidate the reaction mechanism. The yields of intramolecular SN2 fluorination of the veratrole substrates are measured to be very small (<1% in 12 h) in the absence of crown ether promoters, whereas the SN2 fluorination of the substrate possessing a crown ether unit proceeds to near completion (~99%) in 12 h. We also studied the efficacy of intermolecular rate acceleration by an independent promoter 18-crown-6 for comparison. We find that the fluorinating yield of a veratrole substrate (leaving group = −OMs) in the presence of 18-crown-6 follows the almost identical kinetic course as that of intramolecular SN2 fluorination, indicating the mechanistic similarity of intra- and inter-molecular organocatalysis of the crown ether for SN2 fluorination. The calculated relative Gibbs free energies of activation for these reactions, in which the crown ether units act as Lewis base promoters for SN2 fluorination, are in excellent agreement with the experimentally measured yields of fluorination. The role of the metal salt CsF is briefly discussed in terms of whether it reacts as a contact ion pair or as a “free” nucleophile F−.
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16
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Phenol alkylation under phase transfer catalysis conditions: Insights on the mechanism and kinetics from computations. MOLECULAR CATALYSIS 2021. [DOI: 10.1016/j.mcat.2021.111566] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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17
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Pliego JR. Diradical character of the bond breaking in the reaction of Br2 with benzene: Reliable barriers using the CR-CC(2,3) method. COMPUT THEOR CHEM 2021. [DOI: 10.1016/j.comptc.2021.113171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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18
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Catalytic cycle and off-cycle steps in the palladium-catalyzed fluorination of aryl bromide with biaryl monophosphine ligands: Theoretical free energy profile. MOLECULAR CATALYSIS 2021. [DOI: 10.1016/j.mcat.2021.111540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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19
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Pliego JR. The role of intermolecular forces in ionic reactions: the solvent effect, ion-pairing, aggregates and structured environment. Org Biomol Chem 2021; 19:1900-1914. [PMID: 33554992 DOI: 10.1039/d0ob02413a] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The environment enclosing an ionic species has a critical effect on its reactivity. In a more general sense, medium effects are not limited to the solvent, but involve the counter ion effect (ion pairing), formation of larger aggregates and structured environment as provided by the host in the case of host-guest complexes. In this review, a general view of the medium effect on anion-molecule reactions is presented. Nucleophilic substitution reactions of aliphatic (SN2) and aromatic (SNAr) systems, as well as elimination reactions (E2), are the focus of the discussion. In particular, nucleophilic fluorination with KF, CsF and tetraalkylammonium fluoride was used as the main model, because of the importance of this kind of reaction and the recent advances in the study of these systems. The solvent effect, ion pairing, formation of aggregates and formation of complexes with crown ethers, cryptands and calixarenes are discussed. For a deeper insight into the medium effect, many results of reliable theoretical calculations in close agreement with experiments were chosen as examples.
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Affiliation(s)
- Josefredo R Pliego
- Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, 36301-160, São João del-Rei, MG, Brazil.
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